Fertilizer



Jan. 14, 1936. B OBER ErAL Re. 19,825

FERTILIZER Original Filed Feb. 27, 1931 2 Sheets-Sheet l F/aJ.

INVENTOR ,3E/Www A TTORNE YS.

Jn. 14, 1936. B` QBER ET AL Re. 19,825

FERTILIZEH Original Filed Feb. 27, 1931 2 Sheets-Sheet 2 (elli/lar filter/bf [nahm/ea' and mms/@fed Sur/@ce 5ft/far daf/a W [/x Mam;

INVENTORS- BQW uw ATTORNEYS.

sulphuric acid in an open container.

Ressued Jan. 14, 1936 UNITED STATES PATENT OFFICE mmm neven, obasns sama n. wma, enamore,

Md., assignors to The Oberphos Company. Baltimore, Md., a corporation of Maryland Original No. 1,947,138, dated February 13, 1934,. Serial No. 518,851, February 27, 1931. Application for reissue November 15, 1934, Serial N 18 Claims.

This invention relates to the manufacture of phosphate fertilizers and is a continuation in part of prior applications Serial Nos. 117,170 and 172,359, now Patents 1,869,941 and 1,837,329, respectively.

In the processes now used to obtain phosphate fertilizers such as acid phosphate, it is the general practice to treat ground phosphate rock with 'I'his mixture is agitated for a relatively short period and the resulting sludge is deposited in a den. In this den the reaction between the insoluble phosphate and acid proceeds until the mixture sets. It is then transferred to storage sheds wherein it is allowed to remain untilthe reaction is run to completion and the product is cured. Such proceases are uneconomical in that the output is limited by the large time factor involved and the return is small in view of the large outlay in plant.

'I'he primary object of the present invention is to provide a new phosphate fertilizer product. Another object is to provide a granular phosphate fertilizer, the individual particles of which have high mechanical strength.

Yet another object is to provide a proces by which a product of a superior physical condition may be prepared and be readv for immediate use.

A further object is to provide a phosphate fertilizer product of globular or nodular form which is characterized by high percentage available phosphate and a minimal amount of free acid.

A further object is to provide a. phosphate fertilizer product which is immediately readily grindable.

With these and other equally important objects in view, the invention comprehends the treatment of insoluble phosphate with an acid in a closed container in which eective control of the reactions is maintained so as to insure a high acidulation and to produce as an immediate product a material of porous ball form and comprising nodulated or globoid particles of various sizes.

l 'Ihese particles are characterized by relatively high mechanical strength.

To more completely illustrate the improved product, photographs of it are shown in the ac companying drawings, in which:

Figure 1 is a photograph showing the Avariations in actual size of the nodules or particles as actually prepared; and

Figure 2 is a photograph, magniiied ten times. illustrating the vesicular or cellular internal structure and the indurated or encrustrated outer surface.

As disclosed in the prior applications cited above, the process, forexample, may be carried out by simultaneously charging predetermined and respectively proportional quantities of an acid, sunch as sulphuric acid, and finely ground phosphate rock into an autoclave. The autoclave is of the horizontal rotary type and is provided with hollow shafts. Through one of these the charging mixture is admitted and through the other gases or vapors are withdrawn by means of a vacuum pump for the purpose of controlling the pressures in the. ontainer and for evacuating the container for he purpose of drying the product.

After the rock acid mixture has been charged to the container the autoclave is continuously rotated dming the reaction of the material. Due to this rotation the mass within the autoclave is constantly densiiledA and resurfaced, therebybringingthe acid into contact with fresh surfaces of the unattacked phosphate.

The reaction between the tricalcium phosphate and the acid proceeds vigorously and eventuates in gaseous as well as solid products of reaction, The evolution of the steam and gases, if retained, causes a building up of superatmospheric pressures. 'I'hese pressures may or may not be maintained and can be controlled to any desired degree either by withdrawing some of the gases through the vacuum line or releasing them through a suitably positioned blowoif valve.

This reaction between the rock and the acid may be accelerated by applying heat to the mass. 'I'his may readily be done by coursing a heating medium through the hollow thermal jacket of the autoclave. Steam may be employed as the heating medium and when used at a pressure of about ilfty pounds supplies sufficient heat to accelerate the reaction to the optimum degree.

In actual operation, using approximately an 82-100 ratio,vfor example, (82 lbs. of acid calculated as 52 B., to 100 lbs. of phosphate rock dust: actual strength of acid used-54 B.) of acid to dust the mass is maintained in the autoclave for a period of about one-half hour during which the digestion proceeds. Throughout the digestion period, as noted, the material is constantly agitated. In spite of the fact that the products of reaction comprise among other things mono-calcium phosphate and calcium sulphate, the mass is maintained in more or less uent condition, for upon opening the autoclave at the end of a digestion period it is found that the material is not a Asponge-like intumesced structure as in the case of the den processes.

It may be mentioned here that nitrogenous material such as ammonium sulphate o1- urea and/or potash material, such as potassium sui- -phate or carnalite. may be included. as for example. by mixing them with the ground phosphaterockorbydissolvingtheminthesulphiu'ic gases and vapors may be evacuated by opening a blowof! valve on the autoclave and allowing the gases to ilow out for'a period of time sufiicient to reduce the pressure to substantially atmospherlc. If desired, the autoclave may be evacuated by withdrawing lthe gases and vapors through the vacuum line by operating the vacuum pump. In any event, after the blowoi! perlod the autoclave is then evacuated, that is to say is placed under subatmospherlc pressure. In the usual run the vacuum pumpis operated at approximately a 26 to 29 inch vacuum for a period of one-half hour, more or less. During this evacuation period the mass is maintained under agitation by continuing the rotation of the autoclave. To facilitate drying of the material it is desirable in most rims to apply additional heat, although in many instances the sen sible heat of the mass may be of aumciently high value to provide the thermal units necessary for drying. when it is desired to heat the material during the drying period this may be done by coursing steam through the thermal Jacket at a pressure of approximately iifty pounds.

It will thus be seen that for a run of approximately an hour a fertiliser material is completely prepared. A five ton autoclave maybe charged within a period of less than' 'one and one-half minutes. This material may be digested in approximately one-half hour. preferably under superatmospheric pressure of fifty pounds more or less. It will be appreciated that the pressure maybevariedquitewidclyandwillvarydepending upon the type of raw products employed. for with a high carbonate content the pressures tend to increase. The pressure may be maintained at any desired value by intermittently blowing of! during thedigestion period. In or. dinary circumstances, as noted above. a pressure of approximately nity pounds is maintained during digestion.

Thematerialproducedasaremldthisdigestion and vacuum dryingmay immediately be discharged from the autoclave.v In sharpoontradistinction to the den product. and as shown in the drawings, this material is in the form of porous balls or discrete nodules or globules varyinginsisefromverysmallpelletsuptoballs of several inches in diameter. The nodules or ballsshowninrigurelarerepresentativeofthe variation in sise with respect to appearance and external characteristics, but do not depict sctualiy the maximum and minimum sizes. As pointed out hereinbefore, many of the nodules or balls are suiciently small to bc applied directly to the soil without grinding. A characteriaing feature of this product is that the nodules 'orballsthemselvesarequitehardandpossessa high mechanical strength. This mechanical lrengthissohighthatitispoasibletorigorous- ,forty and fifty pounds in the autoclave.

I iy handle the material without disintegration.

This. will be understood, is a decided advan tate and an improvement over the old den produc Another striking characteristic of the product .immediately discharged from the autoclave is that it is encrusted. that is to say the exterior surface is a relatively finely grained dense substance. as shown clearly in Figure 2.

Due to the high mechanical strength of the product and to the variation in size. it is'possible to immediately screen the product and use the fine screenings directly and without grinding for application to the soil. These immediate screenings represent a substantial volume of the total 15 run, 'in many instances ranging between 25 and 50% of tread mass.

"The product is characterized by other advantageous features. as the following example inj "i dicates:

-Acid and dust by weight (using acid calculated as 52? B. but

used as 54 B.) was charged into an autoclave. x

This mass was maintained under continuous agitation and heated under approximately nity L pounds steam pressure for a period of one-half hour. while maintaining pressure of between The autoclave was blown oi! for a period of three to live minutes' and the container then evacuated for a0 about thirty-hva minutes with a vacuum of about twenty-eight inches. During the drying period the autoclave was rotated to continue the agitation of the material and heat applied by maintaining a pressure of iifty pounds of steamin the as thermal Jacket. The product was in -very good condition with a small moisture content co'ntaining a suitable quantity o! very iine nodules and larger nodules or globules of quite uniform sise. There was substantially no adhesion of material to the interior wall of the autoclave.

This material was analyzed one day after the run and showed the following: I

After seven days the material was again analysed and showed the following:

Percentage moisture--. 4.4

It will be noted that the initial or intermediate product is in such condition as to be immediately utilised as a fertiliser, and that after a very brief curing period it is considerably improved. not only because of the reduction in the moisture content'but also because of the increase in total and available PaOs. The brief curing period, as

Percentage moisture ,5;7. Percentage total Px0s---'. 20.0V

Percentage insol. PaOs 1.2 Percentage water sol. PsOs 15.3 Percentage citrate P10 3.5 Percentage acidulation 94.0 Percentage free HsSOl.' 0.2 Percentage freeHsPO 4.1

will be noted, substantially eliminates free sulphuric acid and reduces the free phosphoric acid to avery small percentage. An outstanding chai'- aeteristicoftheprocessiandtheproductisthe high acidulationin viewoftheacidrockratio emnos una 'nu maxaman@ n am" clavesupevrplmsphateisinsuchplusieur-tondi*v tiontbatitisreadilyandconvenientiyminedwith otherfertilisersubrtances.

A'lrheproductobtainedhytheseprocelssare sank other characteristics which markedly differentiate it from the prior superphnsphate prod- .uctspreparedbythedenmethoi Determination oldrillobitg In order to distinguish from superphcsphates prepared hy the ordinary den method and that produced by autoclaving. samples of portions of each product were run through a typical fertiliser drill whlchwas mechanicallydriven and set to distribute the fertilizer at two diii'erent rates. The drilling properties were compared under the same conditions. The rates of flow were calculated to pounds per acre (upon the hypothesis that the drill was drawn at the average speed of threemilesperhour). 'l'heresultsofthesedriiling tests are shown below:

l Bates at which matorm. immun drm impune sommi mung:

v pups ma 17 .amaba Drum?. -fg au ma toda hos hats 17 av A' 0|).v.-x.).--.l. :5.o man It will be noted that with the drill set at either of the two points chon, the rate oi' ilow of the autoclave superphosphate was considerably greater than that for the den superphosphate. Also `this dlilerence in favor of the autoclave superphos'phate was much more marked where the drill was set to deliver at a high rate, for

- under these conditions the natural ow 0f the materials plays an important part. Furtherymore, it was noted, during the course of the tests.

that the now of the autoclave product through the drill was considerably more uniform than that of the den product.

Determination of the anale of repose In addition to the drilling test, the angle of repose of each product was also determined.

' This term means the angle assumed by a conical pile of relatively tine material when it is carefully poured from one source. This angle is the result of the force of gravity and the adhesive force of the material, and in a large measure determines the ease of flow through a drill, since the angle of repose decreases as the ease with which the ilow of material increases. This angle of repose is therefore generally considered to be an accurate criterion of the free owing or drillable qualities of a fertilizer. The results of these tests are as follows:

y l Angle of repose Den superphosphate (17% available P205) 41.0 Autoclave superphosphate (17% available It will be noted that the autoclave superphospaste snowed marked superiority, in angle or repose, over the den product.

In order to further and more completely bring outtinstrikingcharactsrieticsoftheautoclave' 'malumpmorityomtbsden Theseweromade'forthemofmm" were subjected before disintegration to compreslsiontestsixithewellknownrnannier. Theresults ofthesearegivenbelow:

Autoclave cuperphoephate Fresh i4 days old Li, Lbaper a. Sample No 1 n l n l m DIO 2N 423 Fresh 14 days old Lbs. per Lbs. per sq. in eq, in. Sample o. 5. l 23 Sample No. 2 i5. s 37 Sample o. il. 2 27 vulgo l0. 3 29 The superiority of the autoclave superphosphate over the den superphosphate, and particularly when freshly made, is further strikingly' indicated in the following table. As is weil known, theV den superphosphate, when freshly made, can not readily be handled. If it is sub- Jected to any working or pressure, it tends to plasticize or become clayey.' For this reason in the prior manufacture of den phosphate it was necessary to dust the freshly made product with absorbent material, such as ground phosphate rock. In the previous table the average compressive strength of freshly made autoclave superphosphate is about 176 lbs. per sq. inch as against approximately 10 lbs. per sq. inch for the den product. 'I'he difference in tensile strength of the two freshly made products is equally as striking, as shown in the following table.

Tensile strength testautoclave superphosphate To further determine the differential physical characteristics of the two products small billets of each product were tested for penetration by vusing the Gilmore needle test. Inthis deter- 1 lb.' weight. The expressed in mm The results c( these tests are as follows:

Penetration test-autoclave eaperphoephate V4 lb l lb Sample No l----.|mm. No measurable on Peneb'aon test-dea eaperphoephats V lb l lb m No' 1""{4mm. 2l mm.

V4 lbiweight, no penetration was eilected. By increasing this weight to i lb. no measurable impruion was made in the billet. Y

'lhe den product, on the other hand. comparatively to the autoclave product. showed very little resistance to penetration. Even a V4 lb. weight on the needle depressed' it 4 mm. into the den superphosphate, while l lb. depressed the needle 2i mm.

Itwillbenotedfromperusaloithesetests that the autoclave luperphosphate is in a mechanical sense a far superior product to the den superphosphate.

These mechanical characteristics explain the striking superiority oi' autoclave superphosphate by which it may readily and immediately be handled'without any substantial disintegration. The tests on the den product indicate to some extent the reason why freshly made den products so readily plasticise inasmuch as it presents minimal resistance to compression. With any degree of handling at all it tends to break down and iorm a claycy Plastic mass. i Another striking characteristic of the autoclave superpho'sphate is its apparent density. One cubic foot of the autoclave superphosphate contains from 'IB to 80 lbs. of the product, while one cubic i'oo't o! den superphosphate contains only from 55 to 55 lbs. Comparing the two products from the standpoint of apparent specinc volume, it may be stated that if the apparent speciiic volume of the den superphosphate is taken as 1.00. then that of the autoclave superphosphate will be .75. In other words. the ratio oi' the speciiic volume of the autoclave superphosphate to the den superpho'sphate is 3 to 4. The advantages oi this are obvious. The economies eilected in saving on storage space are proportionate tn the apparent density.

It will be noted from representative analyses previously given that the percentage oi available PsOs is approximately higher in autoclave superphosphate than in den vsuperphosphate.

-Thisisduetotwofactors: iirsta lowertotal nmphoaphateposseselmmechanieelprcperties whlchveryaharplyandstrikingiydistinauhhit lrolnthedenpmduct..niismmher ,moreobtainsinthoseiaetonwhiehareotimproducts obtain.

An impressive diitesmsee between the autoclave euperpboepbate and the den product made un under similar conditions oi rock-acid ratio and acidstrengthbthewatercontent. Aswiilbe observed irom the table oi analyst oi Athe two products, the autoclave mperphosphate has less combinedwatenlesstreewaterandconsequently less total water.

'IhemethodiordeterminingtotalwaterisPeneld's method as given in Washingtons book on Analysis oi' Rocks. Dehydrated lime was used in the determination. The term free water is the lo'ss in weight determined at 100 C. According to the A. O. A. C. oiiicial methods the iigures given below unequivocally show that the autoclave material is in iact a dryer product.

Aswillbeseenfromthe ireewatercontent. these products are considerably dryer than the average commercial product. It is interesting to note that although the tree water varies considerably, the percentage o! combined water. whch is the real criterion. shows that theautoclave product has a decidedly lower combined water content than the den suilel'vhosphate.

'rml me om sample Mlm-ul time wat.' wat. w

Den su im ratio using l2. i2 3. 74 a.

w sa? Be. wid. a

Den su 05-100 ratio using 13.7 .8.a 10.01

n s2* ne. add.

man ns-1oo mlousing 1Mo 1.00

p' 52 m. edd. o'

Autoclave su 824m ratio using 8J! L'G o.

D u' ne seid. v

Autoelava super. Siggi ratio on 52 lil M 8. M e. s wne, ma.

VI an' umpa. -ioo nuo um n.1: i12 1.01

w u' Be. wid.

These materials treated were allowed to stand for at least one year between the manufacture and the test. The data given was actually as determined and was not reduced to a common iixed percentage o! P105 for each sample. 'nie available PzOs for these samples oi superphosphate varied substantially from 18.5 to 19. The method used for the iree moisture determinations given in the above table was that given by the A. O. it.l C.

Inasmuch as it is believed by. some investigators that this method. which consists o!v determination of the loss in weight of the sample heated at 100 C. ior iive hours, also possibly drives oi! some oi the combined water, we` have madeireemoisturedeterminationsoi'lossin weight-by heating one sample at C. to constantweightandkeevins anothersampleinan evacuated deeiccator over suiphuric acid at room temperature to constant weight. 'I'he results obtained are given in the following table. The samples used were taken from fairly fresh commercial superphosphates 16% P205.

Free water com Total Vac Sample blned water dess.

M 1ooc. Az 50 o. "n"

Antoclave super..." 10. 25 s. 38 4. 82 6. 4 3. 81 Den super 14. 44 8. 84 6. 14 6. 82 5. Den super 13. 7 8.0 o. 06 6.1 5. 7

Itwill thus be seen that the product of the present invention is new in fact. This novelty apparently resides in a marked differential in physical characteristics as compared to prior products and particularly in those characteristics which materially affect the manipulation, distribution and use of the material. f

When the product which is made by the proc ess disclosed is dried it has a percentage drop in water soluble content of approximately eight per cent. When den superphosphate is dried, it

of approximately thirty-eight per cent. This clearly indicates a great difference in the prod-- uct that is made by our process and the den superphosphate of commerce.

The drying of the den superphosphate and of our product was the same and comprised drying in a rotary drum wherein the material passed from. one end of the drum to the other in from two to three minutes during which time it was subjected to the concurrent flow of hot gases from a coal furnace which contacted with the material. The gases entered the rotary dryer at approximately 1800 F. and left the rotary dryer at approximately 195 to 205 F. The vden superphosphate showed a percentage drop in waterV soluble material referred to in the preceding paragraph under this treatment whereas the product made by our process showed a percentage drop in water soluble material of con siderably less vas indicated.

As 'shown in Figure 1, the product obtained is of porous ball form having a'dense, indurated outer surface and is of internally cellular or vesicular structure, the cells, as depicted, being of varying size and distributed unevenly throughout the mass. The walls of the cells are of a dense hard nature and are relatively thick.

Due to the globulated or nodulated character of the autoclave superphosphate and to the relatively large quantities of small nodules which are formed, the material after being prepared may be directly screened' to obtain a large proportion which is in perfect mechanical condition for direct application to the soil. 'Ihis large percentage of indurated hard ilnes will be appreciated from an inspection of the relatively small size nodules shown in Figure l. Due to its high mechanical strength and its hardness, the entire mass may be rapidly handled immediately after production without any breaking down or plasticlzlng. This, as has been emphasized hereinbefore, very markedly distinguishes this material from the den superphosphate. As has been-explained, the autoclave superphosphate does not cake, and in this factor is Just as sharply distinguished and differentiated from the usual den product. The non-caking qualities of the autoclave superphosphate are largely retained even when fertilizer mixtures are made up with fresh materials. In those factors which are important in the produchas a percentage drop in water soluble content tion and manipulation of the material, the autoclave phosphate manifestly presents strikingly superior characteristics and qualities.

The improvement in this new product over prior den products is further borne out when the factors which are involved in distribution of the material on the soil are considered. The drillability and the angle of repose of the autoclave superphosphate are so markedly better than the den product as to render this difference one almo of kind.

'I'he autoclave superphosphate is in fact free owing. The den superphosphate is not. Due to the free owing characteristics of this autoclave product it can be distributed more uniformly, thereby more emcient fertilization may be secured.

While certain materials have been made. described and tested, it is to be understood that the disclosure of these is given merely to exemplify the improved type of material. considered to reside in the provision of a new phosphate fertilizer as defined in the appended claims.

- We claim:

"1. As a new product, a phosphate fertilizer in porous discrete nodular encrusted and indurated globoid particles, having a crushing strength in excess of several times as great as fully cured den superphosphate.

2. As a new product, a phosphate fertilizer in porous discrete nodular encrusted and indurated globoid particles, having a crushing strength of the order of 170 pounds per square inch or greater when freshly made.

3. As a new product, a phosphate fertilizer in porous discrete nodular encrusted and indurated globoid particles, which has a crushing. strength of the order of 300 pounds per squarer inch or greater.

4. As a new product, a phosphate fertilizer in porous discrete nodular encrusted and indurated globoid particles, having a crushing strength in excess of several times as great as fully cured den superphosphate, and having a tensile strength in excess of ten pounds per square inch.

5. As a new product, a phosphate fertilizer in porous discrete nodular encrusted and indurated globoid particles, having a crushing strength of the order of 170 pounds per square inch or greater a when freshly made, which has atensile strength in excess of twenty pounds per square inch.

6. As a new product, a phosphate fertilizer in porous discrete nodular'encrusted and indurated globoid particles, which has a crushing strength of the order of 300 pounds per square inch or greater, and a tensile strength of the order of 40 pounds per square inch.

7. As a new product, a phosphate fertilizer in porous discrete nodular encrusted and indurated globoid particles, having a crushing strength in excess of several times as great as fully cured den superphosphate, and a weight of the order of 78 pounds per cubic foot.

8. As a new product, a phosphate fertilizer in porous discrete nodular encrusted and indurated globoid particles, having a crushing strength of the order of 170 pounds per square inch or greater when freshly made, and a weight of the order of 78 pounds per cubic foot.

9. As a new product, a phosphate fertilizer in porous discrete nodular encrusted and indurated globoid particles, which has a crushing strength of the order of 300 pounds per square inch or T'he invention is' (ill greater. anda weight o! the orders! 'Il pounds' per cubic toot.

10. An autoclaved processed phosphate tertiliaer comprising densined indurated individual particles which are substantially non-adherent,

andwhieharecharacterisedhyhighcolnpressive s 13. As a new product, a phosphate fertiliser in pom discrete nodular encrusted and indurated glohoid particles. having a crushing strength in excessoi'severaltimesasgrestasfullycured den superphosphate. and containing nitrogenous 13. As a new product, a phosphate fertilimr in porous discrete nodular encrusted and indurated globoid particles. having a crushing strength in'excessofseveraltimesasgreatasiullycured den superphosphate and containing potash and nitrogenous material.

14. Asl a new product. a superphosphate tertlliser in granular discrete particles having a crushing strength in excess o! several times as great as fully cured den superphosphate. formed by crushing the product of claim 1.

15. As a new product, a superphospha tertiliser in porous discrete particles having a crushing strength in excess oi several times as great as fully curedl den superphosphate and a weiht of approximately 78 pounds per cubic foot, formed by crushing the product of claim 1.

16. As a new product. a superphosphate tertiliser in porous discrete nodular encrusted and ihdurated particles having a crushing strength in excess of several times as great u fully cured den superphosphate.

17. As a new product, a superphosphate ierf tiliser in porous discrete nodular encrustated and indurated glchoid particles having a crushing strength in excess' o! several times as great as fully ,cured den superphosphate, and a weight oi approximately 7B pounds per-cubic foot.

18. As a new product. a supernhosphate ferti-v liner in granular discrete particles having a` crushing strength in excess of several-times es great as fully cured den superphosphate. a ten-v sile strength in excs o! 10 pounds per square inch, and a weight or approximately I8 pounds per cubic toot, formed by crushing the product ol claim 1.

BEVERLY om EDWARD n. wran'r. 

